Primary control for burners



m 9 H949- J. .1. ROTHWELL ET AL. A L

PRIMARY CONTROL FOR BURNERS Filed Sept. 6, 1946 I Patented Sept. 6, 1949 2,481,040 PRIMARY CONTROL FOR BURNERS John J. Rothwell and Paul Schell, Elkhart, Ind., assignors to Penn Electric Switch 00., Goshen, Ind., a corporation of Iowa 1 Application September 6, 1946, Serial No. 695,134

16 Claims.

Our present invention relates to an oil burner control or the like, wherein a so called primary control is in the form of a unit to be installed on "the oil pipe in an oil burner nozzle, instead of utilizing the usual stack switch in the stack and wherein there is a so called slip connection, the present application being a continuation-in-part of our co-pending application Serial No. 634,968, filed December 14, 1945.

One object of our invention is to provide a combined combustion switch and safety switch incorporated in the same control unit, which unit may be connected in a burner control circuit in a simple manner So as to deenergize the relay closed circuit of the motor switch as a result of combustion failure either initially or after establishment and further upon failure of a safety heater of the primary control such as a burnt out condition of such heater.

Another object is to provide a primary control that is simple and compact in construction and inexpensive from a manufacturing and installation standpoint, the control requiring'no cutting into the furnace or stack and being so designed as to not interfere with the operation of the usual gun type of oil burner when installed in its nozzle.

A further object is to provide a controller arranged to respond directly to the heat of combustion by exposing a bimetal element thereof to heat in the combustion chamber as radiated back from the burner flame at the discharge end of the burner nozzle, the bimetal being located within a few inches of the discharge end of the nozzle so as to minimize the area of bimetal required for satisfactory operation of the control unit.

Still a further object is to provide a primary control unit in the form of a housing of small size mounted on the oil pipe of the burner and surrounding it so that there is room around the exterior of the housing for relatively free passage of air from the blower to the discharge end of the burner nozzle, a safety heater and a bimetal element responding thereto being located within the housing, the bimetal element being torus shaped to substantially surround the oil pipe and thereby contribute to compactness, the bimetal element having a portion that is directly exposed through an opening in the housing to direct heat from the flame at the discharge end of the nozzle.

An additional object is to provide a combustion switch which utilizes a torus shaped bimetal element in such manner that the single element responds to two different conditions, 1) the comtion heat and (a) the heat from an electrically energized heater, the parts being associated in a control circuit so that the desired opening of the circuit is had upon combustion failure either prior to or subsequent to combustion establishment, and the bimetal being so housed that the ambient temperature surroundingit is stabilized within the housing by the passage of air thereover.

Another additional object is to provide a means to correct for the movement of the bimetal element so that a safety shut-down operation occurs as quickly on a hot-flame failure as it does on a cold-start failure or may be arranged to occur more quickly, thus securing the most satisfactory timing of the primary control for shut down after (1) a long operating period of the furnace (2) a short operating period thereof or (3) non-operation from a cold start, this being accomplished by means of a second bimetal element operating a shutter to variably shield the section of the bimetal element that responds to combustion flame from such flame.

With these and other objects in view our present invention consists in the construction, arrangement and combination of the various parts of a primary control to attain the objects contemplated as well as others which will hereinafter appear in accordance with the following specification taken in conjunction with the accompanying drawings wherein;

Figure 1 is a vertical sectional view through the flame end of a gun type oil burner showing the burner nozzle (oroil tube and oil nozzle), our primary control being mounted on the oil pipe to the oil nozzle and an electric diagram being included to show the relation of our primary control in a burner circuit controlled thereby.

Figure 2 is an enlarged front elevation of the primary control and shows the oil pipe in cross section as taken on the line 22 of Figure 1.

Figure 2a, is a diagrammatic view illustrating the portion of a bimetal element that is exposed to combustion heat in Figure 2.

Figure 3 is a side. elevation of Figure 2 looking from left to right and showing the housing of the primary control in section.

Figure 4 is a sectional view on the line 44 of Figure 3 showing particularly the torus shaped bimetal element,

Figure 5 is a perspective view of a bimetal element for operating the shutter shown in the upper part of Figure 2.

Figure 6 is a bottom plan view of Figure 3 with the housing for the control shown in section, the bimetal element being shown as warped into the position it assumes in response to heat from both an electrical heater and from a combustion chamber, and

Figure '7 is a similar View showing only parts of Figure 6 and illustrating the bimetal warped as a result of electrical heat only, the circuit through the primary control being shown diagrammatically inth-is figure.

On the drawings we have used the reference character B to indicate a mounting base, which base is preferably formed of insulating material;

The base B is in the form of a disc around which ment A. A heater comprising a resistance coil 45 lays in the support 44 and the support has a pair of posts 41 for mounting it on the base 13.

The heater 45 has one end connected as at 52 to the mounting post 32 and its other end connected by a wire 53 to the relay coil BC in Figure 1. The circuit for the heater 45 passes from the post 32 through the bimetal element" A to a contact 54 carried thereby, whi ch'contact is normally engaged with a stationary but adjustable contact 55. The contact 55 is connected by a wire a raised bead i is formed. The base-B- has a central opening in which a-- s l eeve I2 is pressed. v

and the oil pipe is supported along the centerpf an air tube I8 of the burner.

Air is supplied to the air tube l8 from a blower operated by a blower motor BM in the usual mannerv commonly known in the oil burner art. The air tube I8 and the oil nozzle [6 together are usually referred to asa burner nozzle." The burner just'described is usually referred to as being of the gun type.and the oil is sprayed from-the nozzle l6 and ignited by suitable electrodes (not shown) receiving high tension from an electrical ignition mechanism shown diagrammatically in Figure 1 as Ign. I

The tube l8 projects into a combustion chamber of a furnacethewall of which is shown at '20 and this wall is usually lined with refractory 22. T The primarycontrol is telescopically mounted on the oil pipe 14 leading to the oil nozzle i6 and retained in positionrelative thereto by a set screw 26. i I

Cooperatin with the base B is a housing in the form of a cup shaped element 28 against the front of the bead lll and a. cupshaped element 39 of insulation against. the back of the base B. Within the housing section 28 we mount atorusshaped bimetal element A as by anchoring one end to a rigid post by means of a screw 34, the post being fixed :relative tothe'bas'eZB. The bimetal, it will be noted; substantially surrounds the sleeve [2 which makesforcompactness-of design and yet secures-considerable length for the bimetal element w The bimetal element A may be considered as having three sections 38, 40 and-.42.. The section 38 is the one that is anchored at one end by the screw 34. The section 38' may beconsideredas a combustion responsive section because it is open to fiameat the dischargeend of the burner air tube [8. The opening-to permit radiant, heat from the flame to impingethe section- 38 is defined by the housing 28-. which has the lower half closed by a wall 36 that terminates in a half circle flange 31,. as shown in Figure '2 The ends of the fiange31 diverge as at. 39. 'andhave vertical portions 4| at their ends whichlmerge into the cylindrical wall 43 definingthe periphery of the housing --2B. The opening fort-he flame isthat definedby the upper half of the. sleeve [2, the flanges 39 and 4 I and=the upper part of, thecylindrical wall 43 extehding between the upper ends oftheflangeslll; 4

The section 40 of the bimetal element A may be considered relatively non-warping because of a pair of flanges 46 and. 48 formed; along its inner and outer edges. The section 42-0fthe element A may be considered as. a heater section, it being adjacent afchannel-shaped electricheatersupport 44 having its open side toward. the bimetal eleto the room thermostat RT. Obviously the bimetal element A-can be made to operate a separate switch as shown in our copending application, Serial No. 634,968, filed Dec. 14, 1945 instead of-being part of the switch as herein disclosed.

The wires 53 and 56 are part of a room thermostat circuit including the room thermostat and relay coil already referred to, the current for the circuit being supplied by a secondary S of a transformer T. The primary P of the transformer is connected across l-inewires 10 and [2 which supply current for the burner motor BM and for the ignition mechanism Ign. The burner motor and the ignition mechanism are both under control of amotor switch which is normally open, and is closed by therelay-coil whenever it is energized. .7

Within the lower part of the housing 28 a second bimetal element C is provided, this element being anchored at one end in a slot of a post 13 which post extends through the wall 36 of the cover 28 and terminates in a slotted end 14 for adjustment purposes. A lock nut 15 is provided to retain the adjustment. The bimetal element C has an operating arm 15perforated at H to receive 'the lower end of linK IB.

A pivot rod 'l9 extends through the flanges 4! and spans the distance between them. Pivoted thereon is a damper blade having a pair of pivoted ears 8! and 8 2 at its opposite ends. The car 82 has an extension 83 receiving the upper end of thelinlgfw whereby up and downmotion of the bimetal arm 'lfi will cause up and down motion of the extension .83 and resultantmotion of the blade 80 from a cold'position shown by solid lines in Figure 3 to a hot position shown by dotted mes.

PRACTICAL OPERATION Normal burner operation In the operation of our invention, when the parts are in the cold position 'of Figure 3, the contact 54 is held against thecontact 55 by tension in the bimetal element A'as' determined by adjustment of the contact 55. This results inthe room thermostat circuit being closed across'the wires 53 and 56; The secondary circuit of the transformer T is thereby ready for operation whenever the room thermostat RT 010865; When-it does close, then the relay coil RC is energized so that the motor switch MS closes for operating the" burner, and the heater wire--45 is energized because of'the energization of the room thermostat circuit in which the heater'is in-series.

Energization ofthe heater wire 45 causes the bimetal port-ion 42 to become warped or curved and' at the same time heat from the flame of the'burner passing-throughthe opening defined by-theelements 12; 39,11 and 43 effects similar warpage of the bimetal section 38 as in Figure 6 (solid lines). Thedotted" lines in this figure illustrate the cold position of the bimetal'element; Since bothrbimetalelement. sections38 and 42 are warped, the unanchored section 42 will assume approximately the same curvature as the anchored section 38 as shown by the solid lines thus keeping the contact 54 in engagement with the contact 56. I

The combustion chamber temperature will now rise and will cause some rise in temperature ambient to the base B and the housing section 28. This general rise in ambient temperature will cause the bimetal element A to assume an even sharper curvature than that shown in Figure 6 until a maximum temperature is reached if some means is not provided to cut down the heat from the flame. In many tests we have found that such maximum temperature does not exceed approximately 260 F, and therefore the primary control is not heated to a prohibitively high degree as when a combustion switch is located in the stack of a furnace. Therefore lower temperature bimetals may be used and are found more reliable over a long period of time as they are not subjected to undesirable great temperature fluctuations that change the set' in bimetal elements.

After the burner has been operating a few minutes, the second bimetal element Cwill start unwinding, thereby causing the arm 16 to be elevated with the degree of elevation increasing with a rise in temperature. This will swing the damper blade 80 from the inoperative position shown by solid lines in Figure 3, toward the operative position shown by dotted lines, and after some further temperature rise the dotted position will be reached and thedamper can no longer move because of a stop 86 thereon engaging the bottom of a notch 81 some time before the maximum temperature of 260 has been attained.

In the operative position of the damper, it considerably cuts down the effect of the flame on the bimetal element section 38 as the opening from the flame to the bimetal is now defined by the areas 88 and 90 illustrated in Figure 2a, 90 being an opening provided in the damper blade if found necessary due to the blade offering too much shielding effect. 'Obviously the size of this opening also enters into the operation of the device as the size can be changed to meet requirements and the desired results obtained.

Failure of combustion to be established Referrin to Figure 7, if combustion does not occur in the normal manner, the bimetal element section 42 will be heated 'by'its heater 44, thus bending as shown but since there is no flame from the burner there is no heat passing through the opening in the housing 28 to impinge the bimetal element section 38. It accordingly will remain straight and we have a resulting separation of the contact 54 from the contact 55 thus breaking the circuit of the relay coil RC so that the motor switch MS drops open and there by shuts down the burner.

Combustion failure after establishment In the event that combustion is successfully established and then fails, the section 38 of the bimetal element A will straighten out from its curved position as shown by full lines in Figure 6 (sections 38 and 42 being similarly curved) and assume the position of Figure '7 which causes the contact 54 to leave the contact 55 because of the section 42 still being'curved'on account of heat from the heater 44. If the burner has operated only a few minutes the shut down period will have one definite length, whereas if the burner has been operating for a considerable length of time, this period will be substantially the same length due to the damper blade being in the dotted position of Figure 3. If a shorter timing period following long burner energization is desired, the shielding effect of the damper blade can be increased.

By mounting both of the bimetal element sections 38 and 42 within the housing section 28, they are in substantially the same ambient temperature which may fluctuate anywhere between a cold start temperature and temperature attained by long running of the burner, for in stance 260 F. Therefore, the bimetal element is self-compensating for any temperature that it encounters, as ambient temperature affects both sections 38 and 42 equally and merely causes more or less warping without change 'in the position of the actuating end 42 relative to the anchored end 38. The section 42, however, is additionally responsive to the heater 44, whereas the section 38 is additionally responsive to combustion temperature whereby the two sections are brought out of step as indicated by the position of Figure 7 whenever there is combus-- tion failure, either initially or subsequent to the place of both the safety switch contacts and the combustion switch contactsin the usual type of stack switch having a thermal responsive element in the stack, and a safety switch includ ing a heater therefor. In our arrangement, the one bimetal element A responds to both an electrical heater and to temperature in the furnace in such manner that a single set of contacts serve as a safety control in response to combus tion and in response likewise to'failure of the heater 44 such as burning out thereof. Whenever it does burn out, then the room thermostat circuit is open of course and cannot be reclosed until the heater coil is renewed.

Our primary control herein disclosed effects opening of the circuit at the contacts 54 and 55 whenever two events occur at the same time. That is, when the heater 44 is heated and the section 38 of the bimetal element is not heated by combustion. Thereupon, the burner is shut down, whereas during normal cycling of the burner the contacts remain engaged and are never separated. Separation occurs only when there is either an initial or a subsequent flame failure.

Our arrangement eliminates the necessity and use of so called slip connections, in the usual type of stack switch. It has been found very satisfactory in operation throughout rather wide variations in combustion chamber temperatures, and other variable temperature factors may occur without producing a false shut-down by operation of the primary control. The housing of the bimetal element A, and its shape so that it surrounds the oil pipe l4, permit compactness and minimize the overall diameter of the control so as not to interfere with flow of air from aeenoao eb mer toii efl nie, -t mei ei a bimeta elementis properlyzresponsive to ambient temperaturmsothat variation therein does not; p o uce: a f se u d wn; ra and such variations maygbel considerable and yet the de sired shut-down operation will occur whenever there is flame failure from any cause. 7 v

The damperbladfieBflsoperated by the second bimetaleelementC solves very nicely in one way the undesirable ;characteristic of maximum attainable temperature warping the bimetal element-Ase ,far that it considerably lengthens the shut .down timing upon flamefailure after combustion establishment following a long running period pfthel burner. The rate of travel of the thermostatically pperated arm and the size and shapeofthe; damper blade 80 maybe varied to secure the desired results and where the damper has ftoo inuch shielding effect this can be reduced-to the desireddegree as by the use of the openings; Y

While we have shown in the present applicatiomdirect contact of' the contact 54 with the contact,55;;- the himetal elementA may operate a switchthat-rmains in the open position, after once assuming that'position as in our copending application above, ,referred to. Thus the burner control is operableto shut down the systern upon flampe failure ,until such time as the switchis resetimtheclosed positioninstead of serving mereIy;,as-,a=means ;to provide a purging period duringatemporary shut-down period that is terminated-by;theelement A cooling down to normal position andhefiecting re-Vengagement of the ;contact; 5 4 withgthe .contact .55.

Changes may be madetin' the construction and arrangement: of ,theipartsof our device without departing. from. the realsspirit and purpose of our. invention andtit is our intention to cover by our claims any, modifiedvforms of .structure or use (if-mechanical equivalents which may be reasonably-included.within their scope.

We; claim as O'llRiIlVBIltlOIlL 1. A primary control; for burners comprising a base member adapted't'o' be mounted on anon pipein an; oil burnennozzle;v a torus-shaped bimetaLeIement adapted to surround the oil pipe and mountedonsaidbase, said bimetal'element having oneaendanchored,..and the other end free and constituting an; actuating element, a combustion; switch 1 having; switch contacts which are controlled by saidiactuating element, an electric heater; for. saidibimetal-element .to effect warpage of substantiallyrone-half thereof, the other half being adaptedlto' ;be responsive to .direct heat fromthe flameissuing from the oil burner nozzle, a housingaroundboth halves-of said bimetal element and adapted'to surround the oil pipe, said housing adaptedjobe-subiect to ambient temperature within theburner nozzle and having an. opening .throughwhich heat from the flame is adaptedto pass to :thebimetal element, .a normally inoperative damper in said opening, and thermally-responsive; means in said housing adapted to move said damper'to an operative position vshielding said bimetal, element partially from the flame after: theburner operates a sufficientllength of timejor raising the temperature surrounding said primary control to a point somewhat below maximum attainable temperature. Y

2. A; prima ry. contr0l for vburners comprising a base member adapted to be mounted on an oil pipe inan oilelourner.v nozzle, a torus-shaped bi? metal element adapted-ta surround the .oil pipe 8.: -m um r ee is d :b sa:,' ai b m a element having one end-anchored andthepther end free and constituting an actuatingelement a combustion switch; having; switch-contactswhich; are

1 controlled by said actuating element,-an.; electric heater for said bimetal element/Etoeffectlwarpa'ge of substantiallyone-hal-f! thereoftheother-half adapted to be responsive to dire ct--heat from the flame issuing ,from; thesoil burnennozzle, a nor-- mally -inoperative damper {between the; flame and;

said bimetal element I and Y thermally responsive means adaptedfto move said dampers to an (operative position shielding; saidfbimetal element (par, tially upontemperature rise v 3. A primary controlfor, burnersv comprising a base member, adapted to be mounted'in an-oilv burner nozzle, a bimetal element mountedronsaid base, said bimetal-element having one par t anchored, and another; part free-andconstituting an actuating element,- a comb ustion switch having switch contacts whichare controlledby said actuating element, an electric heater for said bimetal element to effectwarpage of one of said parts,- the other of said parts adapted to be-lresponsive to direct. heat fromrthe burner flame, a normally inoperative damper between the flame, and :saidlast mentioned bimetal- ;part, -and. thermallyre-, sponsive means adjacentsthe! flame adapted r to move said dampertc an-pper-atiye position shielde ing said. bimetal element;partial1y;from theflame after the burnentoperates-and before itattainsa stable temperature I 4. A primary controlsforr burners comprising a base member adapted to be mounted, in an oil burner nozzle, a bimetal element mountedcn said base, saidbimetal-element having one part anchored, and another part f reeandbconstituting an actuating element, a c0mbustion-switchhaving switch contacts which are-controlledby said actuating-element, an plectric. heaterfor said bi-, metal element to effect warpageof one-of said parts, the other of .said parts beingadapted to be responsiveto -direct ,heat from the: burner flame, and. means adaptedto reducetheat flow fromthe flame to'said other of said bimetal parts as the combustiQI .;chambertemperature rises;

' 5. A primary controlfor: burners comprising a-housing adapted to be mounted-in anoil burner airtube andhavingjan opening, a torus shaped bimetal element within said housing, saidbimetal element having one-end" anchored, and its other end free and constituting anactuating element, switching mechanism controlled by said actuating element, an electric heater fort-said bimetal element to -efiect.,.warpage of; OIIBp-IJOIfiOn thereof; another portion thereof; being adaptedto be :responsive to direct heat from the flame issuing from the oil burner air tube and passing through said opening to impinge said another portion, and heat responsive; means; adapted to partially shield said opening againstthe passage of heat therethroughas thezoverali temperature of said primary control increases.

6. In a control of the character disclosed, a housing adapted to be mounted in an oil burner air tube-andhavin anopening, a bimetal element within said housing, saidibimetal element havingone'end'anchored;andkits other-end free and constituting an actuating element, t switching mechanism. controlled by. said-actuating element, an electric heater for; saidbimetalelement to effect warpage of-one portion: thereof, another portion thereof being; adaptedito respond to direct heat from the combustion'flame', and burner heat responsive; meansaadaptedxto at least partially 9 shield said opening against the passage of heat therethrough as the temperature of said control increases.

'7. A primary control of the character disclosed comprising a housing adapted to surround an oil pipe within a burner nozzle and located within a few inches of the flame end of the nozzle, a U- shaped bimetal element within said housing, means adapted to shield one arm of said bimetal element'f-rom the flame, said housing having an openin for direct heat rays from the flame to the other arm of said bimetal element, an electrical heater for the shielded arm of said bimetal element, and temperature responsive means adapted to decrease the eifective size of said opening as the temperature within said burner nozzle increases.

8. A control structure comprising a housing adapted to be mounted in a burner nozzle adjacent the flame end of the nozzle, a U-shaped bil metal element within said housing, means adapted to shield one arm of said bimetal element from the flame, said housing having an opening for direct heat rays from the flame to the other arm of said bimetal element, an electrical heater for the shielded arm of said bimetal element, and temperature responsive damper means adapted to choke the size of said opening as temperature increases within said burner nozzle.

9. In a burner control device for a burner system having a burner motor and a switch for operating said burner motor, means adapted to respond to room temperature for effecting closure of said switch, a control circuit adapted to be controlled by the room temperature responsive means and having said control device connected therein, said control device comprising a switch, a heater and a thermal element, a housing therefor, said switch being controlled by said thermal element and its contacts engaged when two individual sections of the thermal element are both heated, said sections being adapted to respond to ambient temperature within said housing, said housing adapted to be located in a burner air tube and having an opening, one of said sections being adapted to respond through said opening to heat from the flame at the end of the air tube, the other section being responsive to heat from said heater, said sections when so responding moving in the same direction and maintaining the contacts of said switch closed whereby heat of the heater and reduction or omission of heat from the flame efiects opening of said contacts, means adapted to effect a decrease in the timing for shut-down when the ambient temperature is high comprising a damper blade located in said opening and variably shielding the same, and means to vary the position thereof to increase the shielding eifect thereof as the temperature increases, said last means being thermally operated by means of a temperature responsive element located within said housing.

10. In a burner control device for a burner system having a burner motor and a switch for operating said burner motor, means adapted to respond to room temperature for efiecting closure of said switch, a control circuit adapted to be controlled by said room temperature responsive means and having the control device connected therein, said control device comprising a switch, a heater and a thermal element, a housing therefor, said switch being controlled by said thermal element and its contacts engaged when two individual sections of the thermal element are both heated, said housing adapted to be located in a burner air tube and having an opening, one of said sections adapted to respond through said opening to heat from the flame at the end of the air tube, the other section being responsive to heat from said heater, said sections when so responding moving in the same direction and maintaining the contacts of said switch closed whereby heat of the heater and reduction or ommission of heat from the flame eiiects opening of the contacts, and thermally responsive means located in said burner air tube and aiTecting said other section for eifect'ing a decrease in the timing for shut-down as the ambient temperature increases.

11. A burner control device of the character disclosed comprising a-combustion switch adapted to surround an oil pipe of a burner and located within a few inches of the flame, a thermal element, said combustion switch having contacts controlled by one end of said thermal element, the other end of said element being anchored, said thermal element comprising two arms both of which are adapted to be subject to ambient temperature, a housing shielding one of said arms, an electric heater for said arm, said housing having an opening through which heat from the flame is adapted to impinge the other arm, temperature responsive means responding to the temperature within said housing for varying the size of said opening, decreasing its size an increase in temperature, said arms when responding to a normal burner operating condition adapted to work equally to maintain said contacts closed whereby heating of the heating element heated arm and a cool or cold condition of the flame heated arm is adapted to move the arms unequally to effect separation of said contacts.

12. A burner control device comprising a combustion switch adapted to be mounted in a burner tube adjacent its discharge end, a thermal element in said combustion switch, said combustion switch having contacts controlled by one end of said thermal element, the other end of said element being anchored, said thermal element comprising two arms, a, housing shielding one of said arms, an electric heater for said arm, said housing having an opening through which heat from the flame is adapted to impinge the other arm, and temperature responsive means adapted to decrease the size of said opening with an increase in temperature in the burner tube.

13. In a burner control device, a combustion switch comprising a pair of thermal element sections arranged in series with one end anchored, contacts controlled by the other end thereof, and a heating element, said contacts being normally in an operative position and remaining so as both of said sections are adapted to warp in response to indirect flame temperature, one of said sections additionally warping in response to heat thereto from the heating element and the other of said sections adapted to additionally warp in response to heat thereto directly from the flame for thereby effecting retention of said sections in operative position, a cooling or cold condition of the flame affected section adapted to render said contacts inoperative, and temperature responsive means adapted to reduce the effect of the flame on the thermal element as the temperature surrounding said burner control device rises.

14. In a burner control device, a combustion switch comprising a pair of thermal element sections arranged in series with one end anchored, contacts controlled by the other end thereof, and a heating element, said contacts being normally in an operative position and remaining so as both of said sections are adapted to warp in response to indirect flame temperature, and adapted to additionally warp in response to heat to one of said sections from the heating element and directly from the flame to the other one which effects retention of said contacts in operative position, a cooling or cold condition of the flame aflected section rendering said contacts inoperative, and temperature responsive means adapted to reduce the eflect of the flame on the thermal element as the temperature of the burner rises.

15. In a primary burner control device, a combustion switch comprising a pair of thermal element sections arranged in series with one end anchored, contacts controlled by the other end thereof, and a heating element, said contacts being normally closed and remaining closed as both of said sections are adapted to warp in response to indirect flame temperature, and adapted to additionally warp in response to heat to one of said sections from said heating element and to the other section direct from the burner flame, thermal responsive means adapted to re duce the action of the burner flame on said other section as the temperature surrounding said control device rises, and a cool or cold flame condition adapted to effect less warpage of said direct flame heated section for opening said contacts for the purpose of shutting down the burner.

16. In a burner control unit, a combustion switch comprising a pair of thermal element sections arranged in series with one end anchored, contacts controlled by the other end thereof, and a heating element, said contacts being normally closed and remaining closed as both of said sections are adapted to be heated equally due to general temperature rise in the burner, and adapted to additionally warp in response to heat to one of said sections from said heating element and to the other section direct from the burner flame, and thermal responsive means adapted to reduce the direct action of the burner flame on said other section as the temperature sur-' rounding said control unit rises.

JOHN J. ROTHWELL. PAUL SCHELL.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date Re. 16,444 Fesler Oct. 26, 1926 1,640,728 Scott Aug. 30, 1927 1,765,056 Cunningham June 17, 1930 1,883,251 Spencer et al Oct. 18, 1932 2,076,968 Shaw Apr. 13, 1937 2,191,640 Beveridge Feb. 27, 1940 2,367,059 Rothwell et a1 Jan. 9, 1945 

